Wind induced noise signals or wind noise presents a significant problem to sound reception in a diverse range of portable electronic equipment for outdoors use such as mobile terminals, hearing instruments, headsets, sound recording cameras etc. Wind noise is often annoying during a conversation where it can lower intelligibility of desired speech signals by auditory masking of important speech cues and during sound recordings where wind noise corrupts fidelity of music recordings.
Wind noise is caused by turbulent airflow around surface features proximate to microphone inlet ports of the portable electronic equipment. These surface features convert a steady flow of wind into turbulent pressure fluctuations which are picked up by the microphones like other, but desired, pressure fluctuations. Investigations into causes of wind noise generation in hearing instruments, that are worn behind the user's ear or in the user's ear canal, have even demonstrated that a part of the wind noise is attributable to turbulence created by the airflow around the ear and head of the user, Dillon, H., Roe, I., and Ketch, R. (1999), “Wind noise in hearing aids: Mechanisms and measurements”, Nat. Acoustic Labs Australia. It follows that combating wind noise by redesign of relevant surface features of the portable electronic equipment alone appears to be an unpromising path.
The spectrum and level of the wind noise induced signals have been shown by the present inventor and others to depend on the wind speed and on placement, shape and dimensions of the portable electronic equipment. However, wind noise is mainly concentrated at low frequencies of the audible frequency spectrum. Earlier reports have shown wind noise spectra that are relatively flat below 300 Hz or below 100 Hz. A prior art mechanism to reduce wind noise has been to place a screen over the microphone inlet ports to reduce turbulence, and many effective windscreens have been developed for sound-recording microphones (Wuttke, J. (1991), “Microphones and the wind”, J. Audio Eng. Soc, Vol. 40, pp 809-817). However, a wind screen is often an impractical solution for many types of portable electronic equipment given the normal severe constraints on size and appearance.